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Astronomers have observed the aftermath of spectacular stellar
explosions known as supernovae before, but until now no one has
witnessed a star dying in real time. While observing supernova 2007uy
with the Swift X-ray Telescope, Alicia Soderberg and Edo Berger
(Princeton University) discovered a mysterious X-ray flash elsewhere in
the galaxy NGC 2770 located about 90 million light years away (Figure 1).
Within a few hours observatories around the world scrambled to study its
light. In a rapid sequence of events the Gemini North telescope was able
to capture and dissect the object’s light in a set of optical spectra
that contains the earliest spectrum ever obtained of a massive star
ending its life in a supernova explosion outside of our galaxy’s
neighborhood.

“We were in the right place, at the right time, with the right telescope
on January 9th and witnessed history,” said Soderberg. “Thanks to the
unique capabilities of the Swift satellite and the rapid response of the
Gemini telescope we were able to observe a star in the act of dying.”

The result of this rapid response, following the January 9, 2008 discovery,
allowed Gemini to provide time-critical spectroscopic observations of the
young supernova and the development of the explosion in a unique sequence of
optical spectra using Gemini North telescope on Mauna Kea in Hawai‘i.

"When I was alerted by Edo Berger shortly after the X-ray outburst, we
didn’t know what it was,” said Jean-René Roy Deputy Director and Head of
Science at the Gemini Observatory. “We immediately agreed to Edo’s
request for Director’s Discretionary time to observe the object.” Roy
approved the program, &ldquo… feeling that we had a unique
opportunity.”

The spectra were obtained with the Gemini Multi-Object Spectrograph
(GMOS) nearly every night between January 11 and 30, 2008 (Figure 2) and
have set a record for the youngest supernova ever captured by optical
spectroscopy other than supernova 1987A which occurred in the satellite
galaxy to the Milky Way known as the Large Magellanic Cloud.

“A few weeks later we had accumulated an outstanding sequence of optical
spectra of a young supernova. I am very pleased that Gemini could work
with the team and play a strategic role in following this unusual
event,” said Roy. These data allowed the team to show that this was a
Helium-rich supernova of a type known as Ibc, and also to measure the
speed of the explosion. The X-ray outburst is interpreted as the
break-out of the supernova shock through the dense wind surrounding the
progenitor star, suspected to have been what is known as a Wolf-Rayet
star.

“We now know what X-ray pattern to look for when a star explodes,” said
Berger. “Hopefully we will be able to find and study many more
supernovae at this critical moment.”

The potential of finding a large number of supernovae at the time of
explosion will also open up avenues of research that previously seemed
nearly impossible. In particular, the determination of the exact
explosion time will allow searches for neutrino and gravitational wave
bursts that are predicted to accompany the collapse of the stellar core
and the birth of the neutron star.

“The next generation of X-ray satellites will find hundreds of
supernovae exactly when they explode, and telescopes like Gemini will
help us study the detailed physics” said Soderberg. “I am thrilled that
our discovery is leading this new wave of astronomy.”

The results will be published in the May 22nd issue of the journal Nature by
lead author Alicia Soderberg (with 37 co-authors) in a paper titled: “An
extremely luminous X-ray outburst marking the birth of a normal
supernova.”

Gemini Observatory GMOS-North Image

Figure 1. Optical image of the host galaxy NGC 2770 obtained with Gemini North (GMOS) on March 6-7th 2008. SN 2008D is indicated. See Image Release for more details on this image and versions of this image without text and at high-resolution for publication.

Figure 2. Sequence of densely-sampled optical spectra from 1.7 to 21 days after the X-ray outburst obtained with the Gemini Multi-Object Spectrograph on Gemini North in Hawaii. There is a clear evolution from a mostly featureless continuum to broad absorption lines, and finally to strong absorption features caused by some elements abundant in the fast expanding shell. From the spectral evolution sequence the supernova SN 2008d is classified as a Helium rich Type Ibc supernova.

Background Information

Most massive stars in the universe end their relatively short lives in
spectacular explosions known as supernovae. Supernovae can outshine a
whole galaxy in brightness. Because there are relatively few massive
stars, these events are rare, on the order of once per century in a
galaxy like ours. Remnants of supernova lead to the formation of black
holes or neutron stars. Unfortunately supernovae are usually detected
only several days or weeks after their explosion, often near maximum
brightness.

Witnessing the birth of a supernova is an extremely rare event, the last
time something similar happened was in 1987 with the nearby supernova in
the Large Magellanic Cloud.

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Hawai'i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in five participant countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the Canadian National Research Council (NRC), the Argentinean Ministerio de Ciencia, Tecnología e Innovación Productiva, the Brazilian Ministério da Ciência, Tecnologia e Inovação and the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT). The observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.